Confirmatory analyses of novel plasma protein associations with the risk of coronary heart disease and stroke will be carried out by applying enzyme-linked immunosorbent assays to baseline plasma specimens from cases and controls in the Women's Health Initiative postmenopausal hormone therapy trials. Candidate proteins were highly ranked in recent in-depth proteomic discovery research. For CHD these are alpha-1-acid glycoprotein 1, thrombospondin 1, complement factor D preprotein, glutathione peroxidase 3, and insulin-like binding protein 1 (IGFBP1). For stroke the candidate biomarkers are IGFBP2, IGFBP6, insulin-like growth factor 2, hemopexin, and beta 2 microglobulin. Specimen analyses will be carried out for 349 CHD cases and for 1-1 matched controls, and for 326 stroke cases and matched controls. Data analyses will control for traditional cardiovascular disease risk factors, and for available biomarkers of inflammation, thrombosis, and lipids. Women developing CHD or stroke following their first year of hormone therapy trial enrollment, and their matched controls, will also have plasma concentrations assessed in 1-year blood specimens for the subset of these proteins found to be affected by estrogen-alone or by estrogen plus progestin in discovery work using the same proteomic platform. The baseline and 1-year protein concentrations will be jointly analyzed to assess the extent to which treatment-related changes in these protein concentrations can mediate hormone therapy effects on CHD and stroke. These analyses will incorporate a novel correction for biomarker measurement error. The project has a high probability of confirming some new biomarkers of CHD and stroke risk, and for providing additional insight into observed hormone therapy effects on these diseases.